Signal transmission method and apparatus for user equipment in mobile communication system

ABSTRACT

A signal transmission method and apparatus of a user equipment for a mobile communication system is provided for improving data transmission reliability and efficiency by transmitting data based on precise discrimination of the uplink transmission resource assignment messages indicative of initial transmission and retransmission. A signal transmission method of a user equipment for a mobile communication system receives an uplink transmission resource assignment message from a base station determines whether a Hybrid Automatic Repeat reQuest (HARQ) buffer is empty, and when the HARQ buffer is empty, transmits to the base station a Media Access Control Protocol Data Unit (MAC PDU) generated with reference to information contained in the uplink transmission resource assignment message.

PRIORITY

This application claims priority under 35 U.S.C. §119(a) to applicationsentitled “SIGNAL TRANSMISSION METHOD AND APPARATUS FOR USER EQUIPMENT INMOBILE COMMUNICATION SYSTEM” filed in the Korean Intellectual PropertyOffice on Aug. 4, 2008 and Sep. 4, 2008, and assigned Serial No.10-2008-0076142 and 10-2008-0087276, respectively, the contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mobile communication system and, inparticular, to a signal transmission method and apparatus of a UserEquipment (UE) for a mobile communication system that is capable ofimproving data transmission reliability and efficiency by transmittingdata based on the precise discrimination of the uplink transmissionresource assignment messages indicative of initial transmission andretransmission.

2. Description of the Related Art

Universal Mobile Telecommunications System (UMTS) is one of the thirdgeneration (3G) mobile telecommunication technologies, which evolvedfrom Global System for Mobile communications (GSM) and General PacketRadio Services (GPRS) systems and uses Wideband Code Division MultipleAccess (WCDMA).

The 3^(rd) Generation Partnership Project (3GPP), which is responsiblefor the standardization of UMTS, is working to significantly extend theperformance of UMTS in the Long Term Evolution (LTE) system. LTE is a3GPP standard that provides for a downlink speed of up to 100 Mbps andis expected to be commercially launched in 2010.

In order to fulfill the requirements for the LTE systems, studies havebeen done in various aspects including minimization of the number ofinvolved nodes in the connections and placing radio protocol as close tothe radio channels as possible.

FIG. 1 is a diagram illustrating an LTE mobile communication system.

As shown in FIG. 1, the LTE mobile communication system utilizes theEvolved Radio Access Network (E-RAN) 110 and 112 having only twoinfrastructure nodes: the Evolved Node B (ENB or Node B) 120, 122, 124,126, and 128 and the Access Gateway (AG) 130 and 132. A User Equipment(UE) 101 accesses the Internet Protocol (IP) network via the E-RAN 110and 112.

The ENB's 120, 122, 124, 126, and 128 correspond to the conventionalNode B which provides the UE 101 with radio access service. The ENB's120, 122, 124, 126, and 128 are responsible for more complex functionsthan that of the conventional Node B. In the next generation wirelesscommunication system, all user traffic including real time services suchas Voice over IP (VoIP) are served through a shared channel. For thisreason, there is a need for a device to collect status information ofthe UE's and scheduling based on the status information. Each of theENBs 120, 122, 124, 126, and 128 is responsible for scheduling the UE's.In order to achieve the speed of 100 Mbps or faster, the wirelesscommunication system exploits the radio access technology of OrthogonalFrequency Division Multiplexing (OFDM) on a 20 MHz bandwidth. Also, anAdaptive Modulation and Coding (AMC) scheme is supported for determininga modulation scheme and a channel coding rate according to the channelstatus of the UE 101.

FIG. 2 is a diagram illustrating a user plane protocol stackarchitecture of an LTE mobile communication system.

As shown in FIG. 2, the UE has a protocol stack including a Packet DataConvergence Protocol (PDCP) layer 205, a Radio Link Control (RLC) layer210, a Media Access Control (MAC) layer 215, and a Physical (PHY) layer220. Also, the ENB has a protocol stack including a PDCP layer 240, aRLC layer 235, a MAC layer 230, and a PHY layer 225.

The PDCP layers 205 and 240 are responsible for IP headercompression/decompression. The RLC layers 210 and 235 pack the PDCPPacket Data Units (PDUs) into a size appropriate for transmission andperforms an Automatic Repeat reQuest (ARQ) function. The data unitdelivered from an upper layer entity is a PDU. The MAC layers 215 and230 serve multiple RLC layer entities. The MAC layers 215 and 230 canmultiplex the RLC PDUs produced by the RLC layer entities into a singleMAC PDU and de-multiplex a MAC PDU into the RLC PDUs. The physicallayers 220 and 225 perform encoding and modulation on the upper layerdata to transmit it through a radio channel and perform demodulation anddecoding on the OFDM symbol received through radio channel to deliver toupper layers.

In the LTE mobile communication system, a Hybrid Automatic RepeatreQuest (HARQ) is utilized for reliable transmission of uplink MAC PDUs.In the mobile communication system using HARQ, when a MAC PDU is notreceived, the receiver transmits a HARQ Non-Acknowledgement (NACK) tothe transmitter such that the transmitter received the HARQ NACKretransmits the MAC PDU. The receiver performs soft combining to combinethe initial transmission and the one or more retransmissions.

In the LTE mobile communication system, uplink resources are allocatedby means of an uplink transmission resource assignment message.

FIG. 3 is a diagram illustrating a message format of an exemplary uplinktransmission resource assignment message.

Referring to FIG. 3, the uplink transmission resource assignment messageincludes a Resource Block (RB) assignment field 305 carrying informationon the amount and position of the resource. In the LTE mobilecommunication system, the resource is assigned in a unit of a resourceblock defined with a predetermined frequency bandwidth of a length of 1msec, and the assigned resources are indicated by the RB assignmentfield 305.

The uplink transmission resource assignment message also includes aModulation and Coding Scheme (MCS) field 310 which indicates theadaptive modulation and coding formats to be adopted to the transmissiondata. This field is 5 bits and can carries one of 29 code pointsindicating combinations of Quadrature Phase Shift Keying (QPSK) and 0.11channel coding rate to 64 Quadrature Amplitude Modulation (64QAM) and0.95 channel coding rate. The rest three code points are used toindicate the Redundancy Version (RV). The MCS field 310 is described inmore detail with reference to Table 1.

TABLE 1 MCS Index Modulation Order TBS Index Redundancy Version I_(MCS)Q′_(m) I_(TBS) rv_(idx) 0 2 0 0 1 2 1 0 2 2 2 0 3 2 3 0 4 2 4 0 5 2 5 06 2 6 0 7 2 7 0 8 2 8 0 9 2 9 0 10 2 10 0 11 4 10 0 12 4 11 0 13 4 12 014 4 13 0 16 4 15 0 17 4 16 0 18 4 17 0 19 4 18 0 20 4 19 0 21 6 19 0 226 20 0 23 6 21 0 24 6 22 0 25 6 23 0 26 6 24 0 27 6 25 0 28 6 26 0 29reserved 1 30 2 31 3

Table 1 is specified in the 3GPP 36.213 V8.6.0 Technical Specificationfor showing the relationship between Transport Block Size (TBS) indexand RV according to the MCS index contained in the MCS field 310.Referring to Table 1, for MCS levels from 0 to 28 indicates RV=0 andrespective TBS indices, and the MCS levels from 29 to 31 indicates RV=1,2, and 3, respectively with no TBS index.

The uplink transmission resource assignment message also includes a NewData Indicator (NDI) 315. The NDI 315 is 1 bit information to indicatewhether the transmission resource assignment message is of either aninitial transmission or retransmission.

The uplink HARQ operation with the NDI of the uplink transmissionresource assignment message is described in FIG. 4.

FIG. 4 is a diagram illustrating a successful HARQ operation in theconventional mobile communication system using the NDI of the uplinktransmission resource assignment message.

Referring to FIG. 4, a UE receives an uplink transmission resourceassignment message 405 at a point in time and transmits a MAC PDU usingthe uplink resource 415 and MCS level indicated by the uplinktransmission resource assignment message 405 after time T 410 elapses.In order to simplify the explanation, the MAC PDU transmitted throughthe resource assigned with the uplink transmission resource assignmentmessage 405 will be referred to as MAC PDU A. Until the MAC PDU A iscompletely transmitted, i.e. before a HARQ ACKnowledgement (ACK) on theMAC PDU A is received or the maximum number of retransmission times isreached, the UE repeats retransmissions 420 and 425 at interval of HARQRound Trip Time (RTT) 417. The MAC PDU A transmission is completed at aspecific point in time, and the UE receives a new uplink transmissionresource assignment message 430 from the ENB. The NDI of the new uplinktransmission resource assignment message is set to a value differentfrom that of the previous uplink transmission resource assignmentmessage 405. If the NDI value change is detected, then the UE regardsthe uplink transmission resource allocation message as a new MAC PDUrequest message and starts transmitting a new MAC PDU, e.g. MAC PDU B,through the uplink resource 435. As aforementioned, the UE repeatstransmission 440 at interval of the HARQ RTT.

In order to manage the transmission resources efficiently, the ENB canassign the different resources for retransmission of the current MACPDU. This technique is called adaptive retransmission. By transmittingthe uplink transmission resource allocation message having the same NDI,the ENB can request the UE for adaptive retransmissions. For instance,if the ENB wants to receive the MAC PDU B through a new RB aftertransmitting the uplink transmission resource assignment message 430,then the ENB transmits an uplink transmission resource assignmentmessage 433 of which NDI (=1) is identical to that of the previousuplink transmission resource assignment message 430 along with the newresource assignment information. If an uplink transmission resourceallocation message of which NDI is identical to that of the previousuplink transmission resource allocation message is received, then the UEdetermines that the adaptive retransmission is requested so as totransmit the MAC PDU B using the newly assigned transmission resource445 and 450.

To determine whether the uplink transmission resource assignment messageis of an initial transmission or retransmission is possible under theassumption that the UE receives all the uplink transmission resourceallocation messages are received successfully.

FIG. 5 is a diagram illustrating a HARQ operation failure in theconventional mobile communication system using NDI of the uplinktransmission resource assignment message.

Referring to FIG. 5, a UE receives an uplink transmission resourceassignment message 505 at a point in time and transmits a MAC PDU usingthe uplink source 515 and MCS level indicated by the uplink transmissionresource assignment message 505 and repeats retransmissions 520 of theMAC PDU at an interval of the HARQ RTT as shown in FIG. 4. Afterreceiving the MAC PDU completely, the ENB transmits a new uplinktransmission resource allocation message 525 of which NDI (=1) isdifferent from that (=0) of the previous uplink transmission resourceallocation message 505. In the case where the new uplink transmissionresource allocation message 525 is lost, the UE may receive anotheruplink transmission resource allocation message 530 having the NDI (=0)identical to that of the previous uplink resource transmission resourceallocation message 505 without being aware of the lost uplinktransmission resource allocation message 525 of which NDI is set to 1.Since the NDI (=0) of the uplink transmission resource allocationmessage 530 is the first message after receiving the previous uplinktransmission resource allocation message 505 in view of the UE and theNDIs of the two successively received messages are identical to eachother, the UE misidentifies that the uplink transmission resourceallocation message 530 is a retransmission request message.

SUMMARY OF THE INVENTION

In order to overcome at least the problems of the prior art, the presentinvention provides a signal transmission method and apparatus for a userequipment (UE) in a mobile communication system that is capable ofimproving data transmission reliability and efficiency of the UE bytransmitting data based on the precise discrimination of uplinktransmission resource assignment messages indicative of initialtransmission and retransmission.

Also, the present invention provides a signal transmission method andapparatus for a UE in a mobile communication system that is capable ofimproving a hybrid automatic repeat request operation of the UE bydiscriminating the uplink transmission resource assignment messagesindicative of initial transmission and adaptive retransmission that aretransmitted by an ENB.

Also, the present invention provides a signal transmission method andapparatus for a UE in a mobile communication system that is capable ofreducing resource waste by running a hybrid automatic repeat requestmechanism with accurate discrimination of uplink transmission resourceassignment messages indicative of initial transmission and adaptiveretransmission that are transmitted by an ENB.

In accordance with an embodiment of the present invention, a signaltransmission method of a user equipment for a mobile communicationsystem includes receiving an uplink transmission resource assignmentmessage from a base station; determining whether a Hybrid AutomaticRepeat reQuest (HARQ) buffer is empty; and transmitting, when the HARQbuffer is empty, a Media Access Control Protocol Data Unit (MAC PDU)generated with reference to information contained in the uplinktransmission resource assignment message to the base station.

In accordance with an embodiment of the present invention, a userequipment for a mobile communication system includes atransmission/reception unit which communicates Physical Downlink ControlChannel (PDCCH) and traffic through a radio channel; a PDCCH processingunit which extracts an uplink transmission resource assignment messagefrom the PDCCH received by the transmission/reception unit; atransmission resource control unit which determines whether the uplinktransmission resource assignment message is indicative of initialtransmission of a new Media Access Control Protocol Data Unit (MAC PDU),adaptive retransmission of a previous MAC PDU, adaptive retransmissionof a new MAC PDU based on a Hybrid Automatic Repeat reQuest (HARQ)buffer status and a New Data Indicator (NDI) and a Redundancy Version(RV) contained in the uplink transmission resource assignment message; aHARQ unit which performs HARQ operation; and an upper layer unit whichprocesses upper layer operations of a Radio Link Control (RLC) device, aPacket Data Convergence Protocol (PDCP) device, and a MAC multiplexer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more apparent from the following detailed descriptionin conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating an LTE mobile communication system;

FIG. 2 is a diagram illustrating a user plane protocol stackarchitecture of an LTE mobile communication system;

FIG. 3 is a diagram illustrating a message format of an exemplary uplinktransmission resource assignment message;

FIG. 4 is a diagram illustrating a successful HARQ operation in theconventional mobile communication system using the NDI of the uplinktransmission resource assignment message;

FIG. 5 is a diagram illustrating a HARQ operation failure in theconventional mobile communication system using NDI of the uplinktransmission resource assignment message;

FIG. 6 is a diagram illustrating a problematic situation that can beencountered in a mobile communication system and solved with a signaltransmission method according to an embodiment of the present invention;

FIG. 7 is a flowchart illustrating a signal transmission method for amobile communication system according to an embodiment of the presentinvention;

FIG. 8 is a diagram illustrating a sequence of Redundancy Versions (RVs)for requesting data retransmission in a mobile communication systemaccording to an embodiment of the present invention;

FIG. 9 is a diagram illustrating how to set RVs for adaptiveretransmission in a mobile communication according to an embodiment ofthe present invention;

FIG. 10 is a flowchart illustrating a signal transmission method for amobile communication according to an embodiment of the present inventionin view of UE;

FIG. 11 is a flowchart illustrating a signal transmission method for amobile communication system according to another embodiment of thepresent invention;

FIG. 12 is a flowchart illustrating a signal transmission method for amobile communication system according to another embodiment of thepresent invention;

FIG. 13 is a diagram illustrating a bundled transmission process of asignal transmission method for a mobile communication system accordingto an embodiment of the present invention;

FIG. 14 is a diagram illustrating a diagram illustrating a bundledtransmission process of a signal transmission method for a mobilecommunication according to another embodiment of the present invention;

FIG. 15 is a flowchart illustrating a signal transmission method for amobile communication system according to another embodiment of thepresent invention; and

FIG. 16 is a block diagram illustrating a configuration of a signaltransmission apparatus of a UE for a mobile communication systemaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the present invention are described in detailwith reference to the accompanying drawings. The same reference numbersare used throughout the drawings to refer to the same or like parts.Detailed descriptions of well-known functions and structuresincorporated herein may be omitted to avoid obscuring the subject matterof the present invention.

In the conventional HARQ mechanism in which a UE uses only the NDI todiscriminate the uplink transmission resource assignment messagesindicative of initial transmission and retransmission, the UE may failto discriminate the messages. In some embodiments of the presentinvention the UE discriminates the uplink transmission resourceassignment messages indicative of initial transmission andretransmission in consideration of the NDI, RV and HARQ buffer status soas to improve the discrimination accuracy.

Typically, the uplink transmission resource assignment messageindicative of an initial transmission of a new packet takes place afterthe previous packet transmission has completed even though the uplinktransmission resource assignment message has the NDI identical to thatof the previous uplink transmission resource assignment message. Inconsideration of this feature, according to some embodiments of thepresent invention, the UE the received the uplink transmission resourceassignment message indicative of initial transmission in a HARQ processcalculates the last available retransmission time and, if the lastavailable retransmission time has expired, flushes the HARQ buffer eventhough the MAC PDU transmission has failed. Also, if the HARQ buffer hasno data when an uplink transmission resource assignment message isreceived in a HARQ process, i.e. the uplink transmission resourceassignment message indicates the first uplink transmission resourceassignment message after flushing the HARQ buffer, then the UEdetermines that the uplink transmission resource assignment message isindicative of initial transmission of a new MAC PDU regardless of theNDI value of the uplink transmission resource assignment message.

FIG. 6 is a diagram illustrating a problematic situation that can beencountered in a mobile communication system and solved with a signaltransmission method according to an embodiment of the present invention.

Referring to FIG. 6, the UE receives an uplink transmission resourceassignment message 605 indicative of an initial transmission of a newpacket for a HARQ process X. Once the uplink transmission resourceassignment message 605 indicative of an initial transmission of a newpacket is received, the UE waits for a time T to elapse from the pointin time at which the uplink transmission resource assignment message isreceived and transmits a MAC PDU 610 using the uplink transmissionresource indicated by the uplink transmission resource assignmentmessage for the HARQ process X. If a NACK 625 is received in response tothe MAC PDU 610, then the UE retransmits the MAC PDU 615. Theretransmission 615 and 620 of the MAC PDU repeats in response to theNACK 625 and 630 at an interval of HARQ RTT. The retransmission can berepeated until a maximum retransmission time is reached. In FIG. 6, theUE receives a HARQ ACK 635 in response to the MAC PDU. Upon receipt ofthe HARQ ACK 635, the UE stops retransmission of the MAC PDU. Next, theUE monitors the maximum retransmission time and flushes the HARQ buffer640 for the HARQ process X when the maximum retransmission time isreached 645. In FIG. 6, an uplink transmission resource assignmentmessage 650 indicative of initial transmission of a new MAC PDU istransmitted for the HARQ process X after the UE has completed thetransmission of the previous MAC PDU 620 but the UE fails to receive theuplink transmission resource assignment message 650. In this case, sinceno MAC PDU is transmitted by the UE, the ENB repeats noise decoding atan interval of the HARQ and determines that the MAC PDU transmission ofthe UE is terminated with a failure when the last availableretransmission time has expired. After some time elapses from thetransmission of the previous uplink transmission resource assignmentmessage 650, the ENB transmits another uplink transmission resourceassignment message 655 indicative of initial transmission of a new MACPDU to the UE, and the UE receives the uplink transmission resourceassignment message 655. In this case, the NDI of the uplink transmissionresource assignment message 655 is set to 0, identical to the NDI of theuplink transmission resource assignment message 605 which the UE hasreceived most recently. If referring to the NDI for discriminatingwhether the uplink transmission resource assignment message 655 isindicative of initial transmission or retransmission, then the UEmisidentifies the uplink transmission resource assignment message 655indicative of initial transmission of a new MAC PDU as an uplinktransmission resource assignment message indicative of retransmission ofprevious MAC PDU. In an embodiment of the present invention the UEchecks the HARQ buffer status in order to avoid such misidentification.If the HARQ buffer is not empty, then the UE discriminates the uplinktransmission resource assignment message with reference to the NDI.Otherwise if the HARQ buffer is empty, then the UE determines that theuplink transmission resource assignment message is indicative of initialtransmission of a new MAC PDU regardless of the NDI.

FIG. 7 is a flowchart illustrating a signal transmission method for amobile communication system according to an embodiment of the presentinvention.

Referring to FIG. 7, a UE receives an uplink transmission resourceassignment message for a HARQ process in step 705. Once the uplinktransmission resource assignment message is received, the UE determineswhether the HARQ buffer for the HARQ process is empty in step 710. Ifthe HARQ buffer is empty, then the UE determines that the uplinktransmission resource assignment message is indicative of initialtransmission of a new MAC PDU, and the process goes to step 715.Otherwise, if the HARQ buffer is not empty, the process goes to step730. At step 730, then the UE determines whether the NDI of the uplinktransmission resource assignment message is toggled, i.e. whether theuplink transmission resource assignment message is indicative of initialtransmission of a new MAC PDU or retransmission of previous MAC PDU.

If the HARQ buffer is empty at step 710, this means that the UE isrequesting to transmit a new PDU using the uplink transmission resourceindicated by the uplink transmission resource assignment message. Atstep 715, the UE checks the Redundancy Version (RV) to determine whetherthe RV is set to 0. The RV set to 0 means that the uplink transmissionresource assignment message is indicative of initial transmission of anew MAC PDU rather than retransmission. If the RV is set to 0, then theprocess goes to step 725. If the RV is set to a value other than 0, thenthe process goes to step 720. Before further progress of theexplanation, the RV is described in more detail with reference to FIGS.8 and 9.

FIG. 8 is a diagram illustrating a sequence of Redundancy Versions (RVs)for requesting data retransmission in a mobile communication systemaccording to an embodiment of the present invention, and FIG. 9 is adiagram illustrating how to set RVs for adaptive retransmission in amobile communication system according to an embodiment of the presentinvention.

Referring to FIGS. 8 and 9, the RV field is used to indicate a part ofthe original data to be retransmitted in the HARQ process. The uplinktransmission resource assignment message indicative of initialtransmission of a new MAC PDU includes the transmission resourceassignment information the MCS level information. The UE that receivedan uplink transmission resource assignment message determines the sizeof the data to be transmitted based on the number of resource blocks andMCS level indicated by the uplink transmission resource assignmentmessage and generates a MAC PDU 805 of the determined size. The MAC PDUis channel-coded according to the MCS level indicated by the uplinktransmission resource assignment message, and the channel-coded data 810is stored in the HARQ buffer for the corresponding HARQ process. The UEtransmits a part of the channel-coded data 810 which is indicated by theRV and performs retransmission in a sequential order of the RV value.

The sequence of RVs is defined to be RV0, RV2, RV3, and RV1, and the UErepeats retransmissions in the sequence cyclically. The RV0, RV1, RV2,and RV3 point to the respective parts 815, 820, 825, and 830constituting the channel coded data 810. In practice, the parts pointedto by the RVs are not continuous unlike the exemplary case shown in FIG.8. In general, the transmission is started from the RV0 815 and then inorder of RV2 825, RV3 830, and RV1 820. The transmission order is cyclicsuch that the data pointed to by the RV1 815 is transmitted after thelast part of the channel coded data has been transmitted. In the case ofan adaptive retransmission, the RV can be indicated in the uplinktransmission resource assignment message indicative of the adaptiveretransmission. For instance, if an uplink transmission resourceassignment message 905 indicative of initial transmission of a new MACPDU is received at a point in time, then the UE transmits the part (ofthe MAC PDU) pointed to by the RV0 915 through the assigned uplinktransmission resource after the time T 910 elapses from the receipt ofthe uplink transmission resource assignment message. Assuming that theMAC PDU is continuously retransmitted, the UE sequentially transmits theparts pointed to by the RV2 920 and RV3 925 through the same uplinktransmission resource at intervals of the HARQ RTT. At this time, if itis required to move the retransmission of the UE to another uplinktransmission resource, then the ENB transmits an uplink transmissionresource assignment message 930 of which NDI is identical to that of theprevious uplink transmission resource assignment message indicative ofinitial transmission of the new MAC PDU. At this time, the ENB maychange the sequential order of the RVs by resetting the value of the RVof the uplink transmission resource assignment message for the adaptiveretransmission. For instance, if the ENB resets the RV of the uplinktransmission resource assignment message for the adaptive retransmissionto 2, then the UE transmits the data pointed to by the RV2 935 althoughit is time to transmit the data pointed to by the RV1, and the changedsequence is maintained until the transmission is completed or thesequence is changed by the ENB again. That is, the sequence is changedsuch that the RV3 940, RV1 945, RV0 950 are sequentially transmittedfollowing the RV2 935. As described above, the RV set to 0 indicatesthat the uplink transmission resource assignment message is indicativeof initial transmission of a new message rather than adaptiveretransmission. Accordingly, the UE generates a new MAC PDU withreference to the information indicated by the uplink transmissionresource assignment message and stores the MAC PDU within the HARQbuffer after channel coding, and transmits a data part pointed to by theRV of the uplink transmission resource assignment message at step 725.

Strictly speaking, the RV can be set to 0 for the uplink transmissionresource assignment message indicative of the adaptive retransmission.For instance, if the uplink transmission resource assignment messageindicative of the adaptive retransmission transmitted to the UE which ispreparing the fifth transmission, then the sequence returns to theoriginal RV sequence so as to be more efficient. Nevertheless, if it ispermitted for the ENB to use the RV0 for the adaptive retransmission,there can be a possibility that the UE may misidentify the uplinktransmission resource assignment message indicative of adaptiveretransmission as the uplink transmission resource assignment messageindicative of initial transmission or vice versa. Accordingly, in theembodiments of the present invention, it is not permitted for the ENB touse the RV0 for adaptive retransmission. In other words, the ENB mustset the RV of the uplink transmission resource assignment message, whichis transmitted at a time reserved for the data pointed to by the RV0 andindicative of the adaptive retransmission, to a non-zero value. Withthis strategy, it is possible to secure the protocol reliability withlittle compromise of transmission efficiency.

Returning to FIG. 7, if the RV is not set to 0 at step 715, then the UEdetermines that the uplink transmission resource assignment message isindicative of adaptive retransmission of a new MAC PDU, and this meansthat an uplink transmission resource assignment message indicative ofinitial transmission of a new MAC PDU is lost before receiving theuplink transmission resource assignment message that is indicative ofadaptive retransmission. As described above, the HARQ retransmission isrestricted to the maximum number of HARQ transmissions. Accordingly,when the uplink transmission resource assignment message indicative ofinitial transmission is lost, the UE does not know how many times theuplink transmission resource assignment message indicative of adaptiveretransmission is transmitted. If the last possible retransmission pointin time is misidentified, then the UE may transmit the data through anunavailable uplink transmission resource that is not reserved for the UEat that time, resulting in interference. Accordingly, if the RV of theuplink transmission resource assignment message is set to a nonzerovalue and the HARQ buffer is empty, then the UE ignores the uplinktransmission resource assignment message and does not transmit data instep 720.

If the HARQ buffer is not empty at step 710, then the UE determineswhether the NDI of the current uplink transmission resource assignmentmessage is toggled as compared to the last previously received uplinktransmission resource assignment message in step S730. If the NDI istoggled, i.e. the NDI of the current uplink transmission resourceassignment message is not identical to the NDI value of the lastpreviously received uplink transmission resource assignment message forthe HARQ process, then the UE determines that the uplink transmissionresource assignment message is indicative of initial transmission of anew MAC PDU and flushes the HARQ buffer in step 735. After flushing theHARQ buffer, the process goes to step 715. Otherwise, if the NDI is nottoggled, then the UE determines that the uplink transmission resourceassignment message is indicative of adaptive retransmission of previousMAC PDU and transmits the part of the coded data, which is stored in theHARQ buffer pointed by the RV, using the uplink transmission indicatedby the uplink transmission resource assignment message in step 740.

FIG. 10 is a flowchart illustrating a signal transmission method for amobile communication system according to an embodiment of the presentinvention in view of UE. The HARQ procedure depicted in FIG. 10 issubstantially similar to that of FIG. 7 but more simplified byinspecting the RV prior to the HARQ buffer inspection.

Referring to FIG. 10, a UE receives an uplink transmission resourceassignment message for a HARQ process X in step 1005. Once the uplinktransmission resource assignment message is received, the UE determineswhether the RV of the uplink transmission resource assignment message isset to 0 in step 1010. If the RV is set to 0, then the UE determinesthat the uplink transmission resource assignment message is indicativeof initial transmission of a new MAC PDU such that the process goes tostep 1015. At step 1015, the UE generates a new MAC PDU and performschannel coding on the MAC PDU based on the information contained in theuplink transmission resource assignment message, stores the channelcoded data within the HARQ buffer, and then transmits the part of thechannel coded data which is pointed to by an RV of the uplinktransmission resource assignment message, i.e. RV0.

Otherwise, if the RV is not set to 0, then the UE determines whether theHARQ buffer for the HARQ process X is empty, i.e. whether the uplinktransmission resource assignment message is indicative of initialtransmission of a new MAC PDU in step 1020. If the HARQ buffer is empty,then the UE determines that the uplink transmission resource assignmentmessage is indicative of adaptive retransmission of a new MAC PDU. Ifthe RV is not set to 0 and the HARQ buffer is empty, this means that anuplink transmission resource assignment message indicative of initialtransmission of a new PDU is lost before receiving the current uplinktransmission resource assignment message such that the UE ignores thecurrently received uplink transmission resource assignment message anddoes not transmit data in step 1025. If the HARQ buffer for thecorresponding HARQ process is not empty at step 1020, then the UEdetermines whether the NDI of the current uplink transmission resourceassignment message is toggled as compared to the NDI value of the lastpreviously received uplink transmission resource assignment message instep 1030.

If the NDI of the current uplink transmission resource assignmentmessage is toggled as compared to the NDI value of the last previouslyreceived uplink transmission resource assignment message, i.e. if theNDI of the current uplink transmission resource assignment message isdifferent from that of the last previously received uplink transmissionresource assignment message, then the UE determines that the uplinktransmission resource assignment message is indicative of the adaptiveretransmission of a new MAC PDU, and the process goes to step 1025. Ifthe NDI is not toggled at step 1030, then the UE determines that theuplink transmission resource assignment message is indicative of theadaptive retransmission of a previous MAC PDU, and process goes to step1035. At step 1035, the UE transmits a part of the channel coded datawhich is stored in the HARQ buffer and pointed by the RV through theuplink transmission resource indicated by the uplink transmissionresource assignment message.

In short, the UE discriminates the following three types of uplinktransmission resource assignment messages and operates depending on thetype of the uplink transmission resource assignment message.

The first type of uplink transmission resource assignment message is anuplink transmission resource assignment message indicative of initialtransmission of a new MAC PDU. When an uplink transmission resourceassignment message of which RV is set to 0 is received for the HARQprocess of which HARQ buffer is empty, the uplink transmission resourceassignment message is determined as the uplink transmission resourceassignment message indicative of initial transmission of a new MAC PDU,whereby the UE transmits the uplink data according to the normal initialtransmission process.

The second type of uplink transmission resource assignment message is anuplink transmission resource assignment message indicative of adaptiveretransmission of the MAC PDU stored in the HARQ buffer. When an uplinktransmission resource assignment message of which the RV is set to anon-zero value and the NDI is not toggled is received for the HARQprocess of which HARQ buffer is not empty, the uplink transmissionresource assignment message is determined as the uplink transmissionresource assignment message indicative of adaptive retransmission of theMAC PDU stored in the HARQ buffer, whereby the UE retransmits the MACPDU stored in the HARQ buffer according to the normal retransmissionprocess.

The third type of uplink transmission resource assignment message is anuplink transmission resource assignment message indicative of adaptiveretransmission of a new MAC PDU. When an uplink transmission resourceassignment message of which the RV is set to a nonzero value is receivedfor the HARQ process of which HARQ buffer is empty or an uplinktransmission resource assignment message of which the RV is set to anonzero value and the NDI is toggled is received for the HARQ process ofwhich HARQ buffer is not empty, the uplink transmission resourceassignment message is determined as the uplink transmission resourceassignment message indicative of adaptive retransmission of a new MACPDU, whereby the UE ignores the uplink transmission resource assignmentmessage and does not transmit data.

In an embodiment of the present invention, an uplink transmissionresource assignment message discrimination method and apparatus usingthe NDI, RV, and HARQ buffer status in bundled transmission is proposed.

FIG. 11 is a flowchart illustrating a signal transmission method for amobile communication system according to another embodiment of thepresent invention. In this embodiment, the UE first inspects the NDI tosimplify the procedure for discriminating the uplink transmissionresource assignment messages.

Referring to FIG. 11, a UE receives an uplink transmission resourceassignment message for a HARQ process X in step 1105. Once the uplinktransmission resource assignment message is received, the UE determineswhether the NDI of the uplink transmission resource assignment messageis identical to or incremented from the last previously received NDI forthe HARQ process X in step 1110. The last previously received NDI can bethe NDI of the last previously received uplink transmission resourceassignment message for the corresponding HARQ process.

If the NDI of the current uplink transmission resource assignmentmessage is incremented compared to the NDI of the last previouslyreceived uplink transmission resource assignment message, i.e. if thevalue of the NDI is changed, the UE determines that the uplinktransmission resource assignment message is indicative of initialtransmission of a new MAC PDU so as to form a new MAC PDU based on theinformation included in the uplink transmission resource assignmentmessage, perform channel coding to the MAC PDU, store the channel codedMAC PDU in the form of channel coded data, and transmit a part of thechannel coded data that is pointed to by the RV of the uplinktransmission resource assignment message in step 1115. At step 1115, theUE forms a new MAC PDU and performs channel coding and stores the newMAC PDU in the HARQ buffer with reference to the information containedin the uplink transmission resource assignment message and transmits apart of the channel coded MAC PDU that the RV of the uplink transmissionresource assignment message points.

If the NDI of the current uplink transmission resource assignmentmessage is identical to that of the last previously received uplinktransmission resource assignment message, the UE determines whether thecorresponding HARQ buffer is empty in step 1120. If the HARQ buffer isempty, the UE determines that the uplink transmission resourceassignment message is indicative of initial transmission of a new MACPDU such that the process goes to step 1115. Otherwise, if the HARQbuffer is not empty at step 1120, the UE determines that the uplinktransmission resource assignment message is indicative of adaptiveretransmission of a previous MAC PDU so as to transmit a part of thecoded data stored in the HARQ buffer, the part being pointed to by theRV of the uplink transmission resource assignment message, using theuplink transmission resource indicated by the uplink transmissionresource assignment message.

FIG. 12 is a flowchart illustrating a signal transmission method for amobile communication system according to another embodiment of thepresent invention. In this embodiment, the UE discriminates the uplinktransmission resource assignment messages indicative of initialtransmission and retransmission with reference to the RV rather thanHARQ buffer status while simplifying the message discriminationprocedure by first inspecting the NDI of the uplink transmissionresource assignment message.

Referring to FIG. 12, the UE receives an uplink transmission resourceassignment message for a HARQ process X in step 1205. Once the uplinktransmission resource assignment message is received, the UE determineswhether the NDI of the uplink transmission resource assignment messageis identical to or incremented from the last previously received NDI forthe HARQ process X in step 1210.

If the NDI of the current uplink transmission resource assignmentmessage is incremented from the last previously received NDI, i.e. ifthe value of the NDI is changed, the UE determines that the uplinktransmission resource assignment message is indicative of initialtransmission of a new MAC PDU so as to form a new MAC PDU based on theinformation included in the uplink transmission resource assignmentmessage, perform channel coding to the MAC PDU, store the channel codedMAC PDU in the form of channel coded data, and transmit a part of thechannel coded data that is pointed by the RV of the uplink transmissionresource assignment message in step 1215.

If the NDI of the current uplink transmission resource assignmentmessage is identical to that of the last previous received uplinktransmission resource assignment message, the UE determines whether theRV of the uplink transmission resource assignment message is set to 0 instep 1220. If the RV of the uplink transmission resource assignmentmessage is set to 0, the UE determines that the uplink transmissionresource assignment message is indicative of initial transmission of anew MAC PDU such that the process goes to step 1215. Otherwise, if theRV of the uplink transmission resource assignment message is set to anonzero value at step 1220, the UE determines that the uplinktransmission resource assignment message is indicative of adaptiveretransmission of a previous MAC PDU so as to transmits a part of thecoded data stored in the HARQ buffer, the part being pointed to by theRV of the uplink transmission resource assignment message, using theuplink transmission resource indicated by the uplink transmissionresource assignment message.

The bundled transmission according to an embodiment of the presentinvention is a feature that a UE retransmits data a predetermined numberof times using an uplink transmission resource to solve the problemcaused by the lack of transmission power at the cell boundary. In thebundled transmission, the UE sequentially transmits the data pointed toby the RV0, RV2, RV3, and RV1 through the identical uplink transmissionresource assigned by the ENB. The ENB performs soft combining on thedata received through four uplink transmissions, error check on thecombined data, and transmits a HARQ ACK or HARQ NACK.

FIG. 13 is a diagram illustrating a bundled transmission process of asignal transmission method for a mobile communication system accordingto an embodiment of the present invention.

Referring to FIG. 13, an uplink transmission resource assignment message1305 indicative of initial transmission of a new MAC PDU is transmittedto a UE configured to operate in a bundled transmission mode. Uponreceipt of the uplink transmission resource assignment message 1305, theUE transmits the data 1315 pointed by the RV0, RV2, RV3, and RV1included in the uplink transmission resource assignment message 1305 forthe four Transmission Time Intervals (TTIs) after the time T has elapsedfrom the receipt of the uplink transmission resource assignment message1305. If a HARQ NACK is received after transmission of the data, thenthe UE retransmits the data 1325 pointed to by the RV0, RV2, RV3, andRV4 at an interval of the HARQ RTT 1320 that is defined for the bundledtransmission.

In the bundled transmission, the same RV is used for the initialtransmission and retransmission. That is, the RV of the uplinktransmission resource assignment message indicative of adaptiveretransmission and the RV of the uplink transmission resource assignmentmessage indicative of initial transmission are identical with eachother. For instance, when transmitting an uplink transmission resourceassignment message 1330 indicative of adaptive retransmission, the ENBsets the RV of the uplink transmission resource assignment message 1330to the RV value of the previously transmitted uplink transmissionresource assignment message 1305. In the case where the same RV is usedfor the initial transmission and retransmission, the UE shoulddiscriminate the uplink transmission resource assignment messagesindicative of initial transmission and retransmission with reference tothe NDI and HARQ buffer status. If an uplink transmission resourceassignment message indicative of initial transmission is lost asaforementioned, it is impossible to discriminate the uplink transmissionresource assignment messages indicative of initial transmission andretransmission only with the NDI and HARQ buffer status. Assuming thatthe uplink transmission resource assignment message 1305 indicative ofinitial transmission is lost such that the UE receives the uplinktransmission resource assignment message 1330 indicative ofretransmission without awareness of the uplink transmission resourceassignment message 1305, the NDI is likely to be toggled in the uplinktransmission resource assignment message 1330 as compared to theprevious uplink transmission resource assignment message 1305.Accordingly, the UE is likely to misidentify the uplink transmissionresource assignment message 1330 indicative of adaptive retransmissionas an uplink transmission resource assignment message indicative ofinitial transmission.

In order to solve this problem, the signal transmission method accordingto an embodiment of the present invention sets the RV to indicate anumber of retransmission times rather than to point to correspondingdata.

FIG. 14 is a diagram illustrating a diagram illustrating a bundledtransmission process of a signal transmission method for a mobilecommunication according to another embodiment of the present invention.

Referring to FIG. 14, when an uplink transmission resource assignmentmessage 1405 indicative of initial transmission and first to thirduplink transmission resource assignment messages 1420, 1430, and 1440indicative of retransmission are transmitted in sequential order, theENB sets the RVs of the uplink transmission resource assignment messages1405, 1420, 1430, and 1440 to 0, 1, 2, and 3, respectively. That is, thevalue of RV increments by 1 from 0 as the number of transmissions ofuplink transmission resource assignment messages increases.

If the RV of the uplink transmission resource assignment message for theHARQ process of which the buffer is not empty is set to a non-zerovalue, i.e. if an uplink transmission resource assignment messageindicative of adaptive retransmission is received without receipt of anuplink transmission resource assignment message indicative of initialtransmission, then the UE ignores the uplink transmission resourceassignment message indicative of adaptive retransmission.

FIG. 15 is a flowchart illustrating a signal transmission method for amobile communication system according to another embodiment of thepresent invention.

Referring to FIG. 15, a UE receives an uplink transmission resourceassignment message for a HARQ process X in step 1505. Once the uplinktransmission resource assignment message is received, the UE determineswhether the RV of the uplink transmission resource assignment message isset to 0 in step 1510. If the RV of the uplink transmission resourceassignment message is set to 0, then the UE determines that the uplinktransmission resource assignment message is indicative of initialtransmission of a new MAC PDU and determines whether the uplinktransmission resource assignment message is indicative of bundledtransmission in step 1513. Whether the uplink transmission resourceassignment message is indicative of bundled transmission is configuredby a control message of an upper layer. If the uplink transmissionresource assignment message is indicative of bundled transmission, thenthe process goes to step 1517. Otherwise, if the uplink transmissionresource assignment message is not indicative of bundled transmission,then the process goes to step 1515. At step 1515, the UE generates a newMAC PDU and performs channel coding on the MAC PDU based on theinformation extracted from the uplink transmission resource assignmentmessage, stores the channel coded data within the HARQ buffer, andtransmits the data pointed to by the RV (=0) of the uplink transmissionresource assignment message. At step 1517, the UE generates a new MACPDU and performs channel coding on the MAC PDU based on the informationextracted from the uplink transmission resource assignment message,stores the channel coded data within the HARQ buffer, and transmits thedata pointed by the RV0, RV2, RV3, and RV1 in sequential order.

If the RV of the uplink transmission resource assignment message is setto a non-zero value, then the UE determines whether the HARQ buffer forthe HARQ process X is empty in step 1520. If the HARQ buffer is empty,then the UE determines that the uplink transmission resource assignmentmessage is indicative of adaptive retransmission of a new MAC PDU. Here,the empty HARQ buffer means that an uplink transmission resourceassignment message indicative of initial transmission of a new MAC PDUis lost after the HARQ buffer is flushed. As aforementioned, the HARQretransmission is restricted to the maximum number of HARQtransmissions. Accordingly, when the uplink transmission resourceassignment message indicative of initial transmission is lost, the UEdoes not know how many times the uplink transmission resource assignmentmessage indicative of adaptive retransmission is transmitted. If thelast possible retransmission point in time is misidentified, then the UEmay transmit the data through an unavailable uplink transmissionresource that is reserved for the UE at that time, resulting ininterference. Accordingly, if the RV of the uplink transmission resourceassignment message is set to a nonzero value and the HARQ buffer isempty, then the UE ignores the uplink transmission resource assignmentmessage and does not transmit data in step 1525. If the HARQ buffer isnot empty at step 1520, the UE determines whether the NDI of the currentuplink transmission resource assignment message is toggled as comparedto the last previously received uplink transmission resource assignmentmessage in step 1530.

If the NDI of the current uplink transmission resource assignmentmessage is toggled, i.e. the NDI of the current uplink transmissionresource assignment message is not identical to the NDI value of thelast previously received uplink transmission resource assignment messagefor the HARQ process, then the UE determines that the uplinktransmission resource assignment message is indicative of retransmissionof a new MAC PDU, and process goes to step 1525. Otherwise, if the NDIis not toggled, the UE determines that the uplink transmission resourceassignment message is indicative of adaptive retransmission of theprevious MAC PDU and determines whether the uplink transmission resourceassignment message is indicative of bundled transmission in step 1533.If the uplink transmission resource assignment message is not indicativeof bundled transmission, then the UE transmits a part (of the coded datapointed by RV0, RV2, RV3, and RV1 within the HARQ buffer) correspondingto the RV of the uplink transmission resource assignment message usingthe uplink transmission resource indicated by the uplink transmissionresource assignment message in step 1535. Otherwise, if the uplinktransmission resource assignment message is indicative of the bundledtransmission, then the UE ignores the RV of the uplink transmissionresource assignment message and transmits the data (MAC PDU) storedwithin the HARQ buffer in sequential order of the RV0, RV2, RV3, and RV1in step 1537.

In short, the UE discriminates following three types of uplinktransmission messages and operates depending on the type of the uplinktransmission resource assignment message.

The first type of uplink transmission resource assignment message is anuplink transmission resource assignment message indicative of initialtransmission of a new MAC PDU. When an uplink transmission resourceassignment message of which RV is set to zero is received for the HARQprocess of which HARQ buffer is empty, the uplink transmission resourceassignment message is determined as the uplink transmission resourceassignment message indicative of initial transmission of a new MAC PDU,whereby the UE transmits the uplink data according to the normal initialtransmission process.

The second type of uplink transmission resource assignment message is anuplink transmission resource assignment message indicative of adaptiveretransmission of the MAC PDU stored in the HARQ buffer. When an uplinktransmission resource assignment message of which RV is set to a nonzerovalue and the NDI is not toggled compared to the previous uplinktransmission resource assignment message is received for the HARQprocess of which HARQ buffer is not empty, the uplink transmissionresource assignment message is determined as the uplink transmissionresource assignment message indicative of adaptive retransmission of theMAC PDU stored in the HARQ buffer, whereby the UE retransmits the MACPDU stored in HARQ buffer according to the normal retransmissionprocess. The UE configured to operate in bundled transmission modeignores the RV of the uplink transmission resource assignment messageand transmits the data stored in the HARQ buffer in sequential order,e.g. the order of the RV0, RV2, RV3, and RV1.

The third type of uplink transmission resource assignment message is anuplink transmission resource assignment message indicative of adaptiveretransmission of a new MAC PDU. When an uplink transmission resourceassignment message of which RV is set to a nonzero value is received forthe HARQ process of which HARQ buffer is empty or an uplink transmissionresource assignment message of which RV is set to nonzero value and theNDI is toggled is received for the HARQ process of which HARQ buffer isnot empty, the uplink transmission resource assignment message isdetermined as the uplink transmission resource assignment messageindicative of adaptive retransmission of a new MAC PDU, whereby the UEignores the uplink transmission resource assignment message and does nottransmit data.

FIG. 16 is a block diagram illustrating a configuration of a signaltransmission apparatus of a UE for a mobile communication systemaccording to an embodiment of the present invention.

Referring to FIG. 16, the signal transmission apparatus includes anupper layer unit 1605, a HARQ unit 1610, a transmission resource controlunit 1620, a transmission/reception unit 1625, and a PDCCH processingunit 1630.

The transmission/reception unit 1625 is responsible for receiving aPhysical Downlink Control Channel (PDCCH) through a radio channel andcommunicating other traffic. The transmission/reception unit 1625decodes the signal received on the PDCCH and outputs the decoded signalto the PDCCH processing unit 1630.

The PDCCH processing unit 1630 performs a CRC check on the decode signaloutput by the transmission/reception unit 1625 and outputs the uplinktransmission resource assignment message that passes the CRC check tothe transmission resource control unit 1620. The transmission resourcecontrol unit 1620 extracts the NDI and RV from the uplink transmissionresource assignment message and discriminates the uplink transmissionresource assignment message indicative of initial transmission of a newMAC PDU, adaptive retransmission of the MAC PDU stored in the HARQbuffer, and adaptive retransmission of a new MAC PDU with reference tothe NDI, RV, and the HARQ buffer status. If the uplink transmissionresource assignment message is indicative of initial transmission of anew MAC PDU, the transmission resource control unit 1620 controls theupper layer unit 1605 to determine the size of the MAC PDU to betransmitted with reference to a number of assigned transport blocks andMCS level, generate the MAC PDU of the determined size, and deliver theMAC PDU to the HARQ process. If the uplink transmission resourceassignment message is indicative of adaptive retransmission of theprevious MAC PDU, the transmission resource control unit 1620 controlsthe HARQ unit 1610 to perform the adaptive retransmission of theprevious MAC PDU. If the uplink transmission resource assignment messageis indicative of adaptive retransmission of a new MAC PDU, thetransmission resource control unit 1620 ignores the uplink transmissionresource assignment message and does not transmit data.

The upper layer unit 1605 represents the PDCP layer device andmultiplexer of MAC layer. The HARQ unit 1610 includes a plurality ofHARQ processes and performs HARQ operation for each of the HARQprocesses.

As described above, the signal transmission method and apparatus for amobile communication system according to the present invention enables aUE to accurately discriminate the uplink transmission resourceassignment messages indicative of initial transmission andretransmission of data, thereby reducing a waste of resources caused bya misidentification of the uplink transmission resource assignmentmessage.

Although embodiments of the present invention have been described indetail hereinabove, it should be clearly understood that many variationsand/or modifications of the basic inventive concepts herein taught whichmay appear to those skilled in the present art will still fall withinthe spirit and scope of the present invention, as defined in theappended claims.

1. A signal transmission method of a user equipment for a mobilecommunication system, comprising: receiving an uplink transmissionresource assignment message including a New Data Indicator (NDI) torepresent whether the uplink transmission resource assignment message isfor an initial transmission, and a Modulation and Coding Scheme (MCS)index to represent a modulation order, a Transport Block Size (TBS)index, and a Redundancy Version (RV) from a base station; determiningwhether a Hybrid Automatic Repeat reQuest (HARQ) buffer is empty; andwhen the HARQ buffer is empty, transmitting to the base station a newMedia Access Control Protocol Data Unit (MAC PDU) based on the uplinktransmission resource assignment message.
 2. The signal transmissionmethod of claim 1, further comprising checking whether a value of the RVis set to 0, and when the value of the RV is set to 0, sending the newMAC PDU.
 3. The signal transmission method of claim 1, furthercomprising checking a size of transport block assigned by the basestation with reference to the MCS index contained in the uplinktransmission resource assignment message after determining whether aHARQ buffer is empty, and when the size of transport block can beidentified, sending the MAC PDU.
 4. The signal transmission method ofclaim 2, further comprising ignoring the uplink transmission resourceassignment message when the RV is set to a nonzero value.
 5. The signaltransmission method of claim 1, further comprising: determining, whenthe HARQ buffer is not empty, whether the NDI of the uplink transmissionresource assignment message is toggled; and retransmitting, when the NDIis not toggled, the MAC PDU using a transmission resource indicated byand with reference to a Redundancy Version of the uplink transmissionresource assignment message.
 6. The signal transmission method of claim5, further comprising: flushing, when the NDI is toggled, the HARQbuffer; and determining whether the RV of the uplink transmissionresource assignment message is set to
 0. 7. The signal transmissionmethod of claim 6, further comprising: transmitting, when the RV is setto 0, a new MAC PDU to the base station using the transmission resourceand the MCS index indicated by the uplink transmission resourceassignment message; and ignoring, when the RV is set to a nonzero value,the uplink transmission resource assignment message.
 8. A user equipmentfor a mobile communication system, comprising: a transmission/receptionunit which communicates a Physical Downlink Control Channel (PDCCH) andtraffic through a radio channel; a PDCCH processing unit which extractsan uplink transmission resource assignment message from the PDCCHreceived by the transmission/reception unit; a transmission resourcecontrol unit which determines whether a Media Access Control ProtocolData Unit (MAC PDU) to be transmitted is a new MAC PDU or a previous MACPDU based on at least one of a Hybrid Automatic Repeat reQuest (HARQ)buffer status, a New Data Indicator (NDI) and a Redundancy Version (RV)contained in the uplink transmission resource assignment message; a HARQunit which performs a HARQ operation; and an upper layer unit whichprocesses upper layer operations of a Radio Link Control (RLC) device, aPacket Data Convergence Protocol (PDCP) device, and a MAC multiplexer.9. The user equipment of claim 8, wherein the transmission resourcecontrol unit determines, when the RV is set to 0, that the uplinktransmission resource assignment message is indicative of initialtransmission of a new MAC PDU, decides a size of the MAC PDU to betransmitted based on a Modulation and Coding Scheme (MCS) levelcontained in the uplink transmission resource assignment message,controls the upper layer unit to generates the MAC PDU, and delivers theMAC PDU to the HARQ unit.
 10. The user equipment of claim 8, wherein thetransmission resource control unit determines, when the HARQ buffer isempty and the RV is set to a nonzero value, that the uplink transmissionresource assignment message is indicative of adaptive retransmission ofa new MAC PDU and ignores the uplink transmission resource assignmentmessage.
 11. The user equipment of claim 8, wherein the transmissionresource control unit determines, when the HARQ buffer is not empty,whether the NDI is toggled, and determines, when the NDI is not toggled,that the uplink transmission resource assignment message is indicativeof adaptive retransmission of a previous MAC PDU, and retransmits theprevious MAC PDU using a transmission resources and RV indicated by theuplink transmission resource assignment message.
 12. The user equipmentof claim 11, wherein the transmission resource control unit flushes,when the NDI is toggled, the HARQ buffer, transmits, when the RV is setto 0, a new MAC PDU using a transmission resource and a Modulation andCoding Scheme (MCS) level indicated by the uplink transmission resourceassignment message to a base station, and ignores, when the RV is set anonzero value, the uplink transmission resource assignment message.